Monofilament testing for screening and monitoring of peripheral nerve function is long established. It has been shown that filaments are a sensitive monitor means for the testing of the peripheral nerve function of a patient, particularly hand and feet body areas. In the 1800's the focus of peripheral nerve testing of the hands was on the study of normal physiology and horsehairs were used as filaments to measure only light thresholds of touch recognition.
In the late 1950's it was determined that a broader range of filament forces were needed than those available with horsehairs to refine the filament method for peripheral nerve testing. J. Semmes and S. Weinstein designed and developed nylon monofilaments of increasing diameter for peripheral nerve testing with such filaments set at right angles proximate the end of acrylic (Lucite) rods. Such rods, or filament handles, are of approximate pencil length for holding and manipulation by the hand of a therapist or health care examiner measuring the peripheral nerve function of the fingers of a patient.
The Semmes-Weinstein (S-W) monofilament testing devices have become the standard means for repeatable testing and measurement of the threshold of cutaneous sensory perception. Through the 20 unit series of testing devices a trained hand therapist or health care examiner can distinguish in a patient between: light touch, diminished light touch, diminished protective sensation, loss of protective sensation, and deep pressure sensation. The series of nylon monofilaments (of uniform 38 mm length) are sized and numbered to correspond to Log(10× force in mg) of force. Lowest force in the series is 4 mg and the highest force is 447 grams. The monofilaments (of constant length, but of increasing diameters) are designed to bend when a specific value of force is reached and such design provides unique control of, and creditability to, the S-W sensory test method. Thus, the series of S-W test devices provides an accurate method by which both diminishing and returning sensation of a patient's body surfaces and extremities can be evaluated and allows the health care examiner to predict and interpret the patient's levels of nerve function and sensibility.
The well known S-W monofilament test units have been marketed as a full 20 unit series or as a set of 5 units having selected sensory level designations of 2.83, 3.61, 4.31, 4.56 and 6.65. Although the S-W monofilament test devices may be used to evaluate sensory levels of body areas and extremities of patients, they are bulky to store, carry and manipulate.
The hand held peripheral nerve function test instrument described in U.S. Pat. No. 5,823,969 to Christy (the '969 patent) addresses some of the shortcomings identified above. This instrument includes a handle of approximate pencil length and configuration with a pivotal forward head portion. A monofilament element projects from the forward head portion of the instrument for application to a body surface area for evaluating the patient's sensory perception thereof. The pivotal forward head portion of the instrument is positionable between two points of filament orientation. The first position of the head portion of the instrument results in projection of the monofilament element in a test evaluation position where the filament element extends downwardly from the handle at an angle of about 90 degrees. The second position of the head portion of the instrument results in projection of the monofilament element in a non-testing position with the filament element extending in a protected position along the length of the handle.
The '969 patent describes a number of benefits including but not limited to providing (1) a convenient shape when not in use with the monofilament elements protected from undesired bending or buckling forces, (2) an elongated handle and forward pivot head bearing the monofilament test element, and (3) an elongated handle with a two-position forward pivot head bearing the monofilament test element with the pivot head being snap-set positionable to place the monofilament element in a downwardly vertical test position at right angle orientation with respect to the handle and alternatively to place the monofilament element in a position within the handle whereby the filament element is protected from undesired bending and buckling forces during periods of non-use of the instruments.
Notwithstanding the above, various improvements to a tactile sensory testing instrument are still desired including but not limited to: (1) increased protection of the monofilament testing element when the instrument is not in use; (2) decreased static charges on the monofilament which may cause undesirable displacement or migration of the monofilament; and/or (3) a more robust pivotable joint.
Other objects and advantages of the invention will be apparent from the following summary and detailed description of the invention, taken together with the accompanying figures.